fbcon: Add an option to disable fbcon in panic

This is required to avoid conflict between DRM_PANIC, and fbcon. If
a drm device already handle panic with drm_panic, it should set
the skip_panic field in fb_info, so that fbcon will stay quiet, and
not overwrite the panic_screen.

Signed-off-by: Jocelyn Falempe <jfalempe@redhat.com>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Link: https://patchwork.freedesktop.org/patch/msgid/20240717090102.968152-3-jfalempe@redhat.com

drivers/video/fbdev/core/fbcon.c

@@ -270,12 +270,17 @@ static int fbcon_get_rotate(struct fb_info *info)
 	return (ops) ? ops->rotate : 0;
 }
 
+static bool fbcon_skip_panic(struct fb_info *info)
+{
+	return (info->skip_panic && unlikely(atomic_read(&panic_cpu) != PANIC_CPU_INVALID));
+}
+
 static inline int fbcon_is_inactive(struct vc_data *vc, struct fb_info *info)
 {
 	struct fbcon_ops *ops = info->fbcon_par;
 
 	return (info->state != FBINFO_STATE_RUNNING ||
-		vc->vc_mode != KD_TEXT || ops->graphics);
+		vc->vc_mode != KD_TEXT || ops->graphics || fbcon_skip_panic(info));
 }
 
 static int get_color(struct vc_data *vc, struct fb_info *info,

include/linux/fb.h

@@ -510,6 +510,7 @@ struct fb_info {
 	void *par;
 
 	bool skip_vt_switch; /* no VT switch on suspend/resume required */
+	bool skip_panic; /* Do not write to the fb after a panic */
 };
 
 /* This will go away